Theresa May told she should not shrug off concerns about Donald Trump simply to bolster special relationship.
Photograph: Will Oliver/EPA

Theresa May is facing growing pressure, including from high-profile Conservatives, to warn Donald Trump that the British government considers his comments about torture to be unacceptable.

MPs and peers have lined up to urge the prime minister to use her first meeting with the US president to take a stand, amid claims that any return to controversial torture techniques would seriously damage intelligence cooperation.

Trump and May will give a joint press conference after their meeting, the White House said on Thursday. It will be Trump’s first conference as president, and comes as something of a surprise, after Number 10 sources played down the prospect of such an event earlier this week.

“How can the UK claim the relationship is special when it potentially involves torture,” he told the Guardian. “Theresa May must raise this with President Trump and explain the extremely damaging consequences that this policy would have on intelligence cooperation between allies.”

He argued that it would call into question the ways intelligence agencies work together, with a mutual understanding that information is never obtained via such techniques.

Responding to Trump’s claim that tactics such as waterboarding work and might be considered legal, Robertson added: “If you had anyone who was in a situation where for days or weeks they experienced drowning they will tell you anything.”

Another member of the intelligence and security committee, Labour MP Gisela Stuart, argued that Trump could not ignore the security relationship with the UK.

“I think [the prime minister] should raise it as a reminder that post-Bush we thought we had an agreement that this was unacceptable to the British services, and that it would make relations very difficult if there was any going back on that,” she said.

“We have made it absolutely clear that water-boarding is unacceptable. I think we should make it clear don’t go there.”

It came as an open letter to the prime minister from the campaign group, 38 degrees, calling on her to stand up to Trump built momentum - with over 20,000 signatures, expected to rise to 100,000.

“The British stand firm against tyrants and bullies. We oppose torture anywhere in the world, we believe that women deserve equal rights, and brilliant British scientists are leading the fight against climate change,” said campaigns director, Laura Townshend.

The comments came alongside interventions from the Labour leader, Jeremy Corbyn, who tweeted:

And Andrew Tyrie, the MP who chairs the Treasury select committee, asked May to make clear to her American counterpart that “in no circumstances will she permit Britain to be dragged into facilitating that torture, as we were after September 11th”.

He added that any US return to rendition and torture would “be not just illegal and immoral but counterproductive” and make gathering intelligence more difficult.

May assured Tyrie on Wednesday that Britain has a clear position on the issue. “We do not sanction torture, we do not get involved in that, and that will continue to be our position,” she said. The comments have been reiterated by the Brexit secretary, David Davis, and the foreign secretary, Boris Johnson, but there has been no suggestion that the prime minister will raise the issue in a meeting with Trump.

Meanwhile, a former key adviser to David Cameron has told the Guardian that the previous prime minister would have been minded to raise the issue in a meeting with an American counterpart.

“It is really difficult and we would have been wringing our hands about. There is no upside to the UK falling out with the US and David would have been pragmatic,” they admitted. “But he always believed that a good friend was an honest friend, and Britain has not changed its position on torture.”

They said Cameron’s team had been “pretty brave” during international trips, raising the case of Gary McKinnon in the US, and choosing to wear poppies in Beijing on Remembrance Day despite warnings that their significance in the opium wars could cause offence.

The former adviser said they expected May would raise the issue, as she had shown she was willing to speak out.

Others in parliament added to the pressure. Former Labour leader Ed Miliband said the prime minister “bears a huge responsibility” to respond to comments that he called reprehensible.

“She should stand with Republicans like John McCain who are horrified by the president’s comments. Kowtowing to Donald Trump, whatever his latest outrage, is not in Britain’s interests,” he said, arguing that the relationship must be based on shared values.

Toby Harris, Labour’s former leader on the London assembly, admitted it was an “incredibly difficult” situation because the government was desperate to support the US. But he added: “There is no doubt that Britain’s position on these matters should be made clear.”

Vernon Coaker, a former shadow defence secretary, agreed: “The lesson of history is that if you abuse human rights, and resort to the methods of the terrorists, it doesn’t help.” He said May had spoken out on Trump’s misogynistic comments and must now do so again.